Not having seen the original Tron in a long time, I felt a little bit lost at first. Not enough to ruin the movie for me, though. It was more along the lines of I wish I'd watched the original first, so I could get the continuity of the story and understand the whole "the grid" thing more in-depth. The effects were awesome, the story was really well-written, and did I mention the effects were awesome? I love Jeff Bridges, so it was nice to see him come through in this role, man. :) Overall, it was really, really, good. I'm glad I saw it in 2D, though, or I may have thrown up!
As a fan of the books, I was really pleased with the execution of this film. There were several really poignant scenes that truly showed how much these characters (and young actors) have grown, and brought the film to an entirely new level. Well worth the 2.5 hours!